A vehicle power source device in the following is developed. In the vehicle power source device, plural batteries which are different in the electric characteristics, for example, a lead batter and a lithium ion battery are connected in parallel, then the lithium ion battery has a higher energy density than the lead batter. (see patent literature 1)
In the power source device of patent literature 1, the lead batter is connected to the lithium ion battery as a high energy density battery. In this power source device, without via a DC/DC converter, the lead battery and the lithium ion battery are connected in parallel. In this power source, both the lead battery and the lithium ion battery are charged by a generator, and also provide electric power to a vehicle side load. In addition, the above power source device enables to get the excellent electric characteristics which one of them cannot get by the parallel connection of the lead battery and the lithium ion battery which are different in the electric characteristics. For example, the lead battery is inexpensive, and its charge and discharge capacity is large, and enables excellent large discharge current characteristics. For example, the lithium ion battery has a high capacity compared with weigh or volume, and is efficiently charged with a large current from a generator. Therefore, the power source device of the parallel connection of the lead battery and the lithium ion battery which are different in the electric characteristics enables the excellent characteristics which only the lead battery cannot enable.